High-frequency signaling



- Dec 11, 1928.

E. PETERSON HIGH FREQUENCY SIGNALING Filed Dec. 15, 1923 Patented Dec.11, 192 8.

UNITED STATES 1,695,058 PATENT oFF cE. I

EUGENE PETERSON, OF NEW YORK; N. Y., ASSIGNOR TO WESTERN ELECTRIC COM-PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

HIGH-FREQUENCY SIGNALING.

Application filed December 15, 1923. Serial No. 680,810.

This invention relates to high frequency signaling and particularly toWavemodifying systems. I

i It is an object of the invention to produce in a novel and effectivemanner, modulation of high frequency waves by a signal or other controlwave, either for transmission or reception.

More specifically the invention relates to a systemin which a highfrequency carrier wave is modulated in accordance with currentsof'speech frequency, thereby giving to the high frequency oscillations aspeech sig" nal wave form, some or all of the products of modulationthen being impressed upon the transmission line. i

In accordance with a feature of the invention, a modulating system isemployed having a speech amplifier tube, an oscillator tube and ifdesired a third tube serving as an am I plifier for the side band. Thespeech ampliing upon the phase relation between the side bands producedin the two tubes.

The various features and advantages of the invention will be apparentfrom the following description taken in connection with th eaccompanying drawing, in which:

Fig. 1 is a diagrammatic illustration of a carrier transmission systemshowing the method of coupling the speech amplifier and oscillator tubesto the transmission line when the side bands produced in the two tubesare in phase. i I

Fig. 2 represents a carrier transmission system showing the method ofcoupling the two tubes when the side bands produced in the tubes are outof phase.

Fig. 3 illustrates a modification of tem shown in Fig. 2.

Referring in detail to Fig. l, amicrophone 1 is included ina circuit 2,such as a telephone the syslinc, in which are produced low frequency 1signaling waves to be transmitted'by modu lating a high frequencycarrier'wave. The low frequency circuit 2 is coupled by means of atransformer 3.to the input circuit of a modulating system including aspeech amplifying tube 4, an oscillator tube 5; and an amplifier tube 6serving as an amplifier for the side band. Plate voltage issupplied tothe speech amplifier tube 4 by a source of current 7 through one'windingof a transformer 8. and plate. voltage is supplied to the oscillatortube 5 by a similar source 9 through the other winding of thetransformer. The transformer 8 serves to couple the plate circuits forthe variation currents so that the speech variations are impressed onthe oscillator; and the carrier oscillations are impressed on thespeechamplifier. The purposeand effect of this coupling will be pointedoutherein- 5 after.

The oscillator may have any desired circuit arrangement for theproduction of continuous waves tobe modulated." As shown, the

input circuit of the oscillator tube 5 includes a coil 10 which'isconnected between its cath ode and control element. The tuned circuitfrequency of the oscillations generated. The coil 11 is coupled to thecoil 10 and, as indi-.

cated by the arrow the condenser 12 may be adjusted to vary the periodof the tuned circuit and hence the frequency of theoscillationsgenerated. A resistance 13-is included between the oscillator anode andthe tuned oscillatory circuit to limit the amplitude of the highfrequency waves supplied from-the oscillator output terminals to the"tuned circuit 11, 12 inaccordance with usual practice;

As stated. hereinabove; the high frequency carrier current generated inthe oscillator tube 5 is transmitted tothe' speech amplifier tube 4, andthe amplified speech 'currents'are likewise transmitted to theoscillator tube '5. Consequently modulation takes place; in

the speech amplifier tubeas well as in the oscillator. I I I It has beenfound'that where modulation results; as in the-present case,from'op'erating over the non-linear portion of thevolt-am- I pcretubecharacteristic, the modulation components from two tubesassociated"according to the invention will be e ther in phase agree- 7O ofthespeech amplifiera'nd oscillator tubes i ment or in phase opposition.Heretofore in coupled-plate-circuit modulating systems in which themodulating action has been con fined to one tube, it has only beennecessary to couple the load circuit to one tube. IVhere modulation isproduced in each of a plurality of tubes, in accordance with theinvention, however, it is necessary to connect the load circuit to thetwo tubes in such a way that the modulating effect of one tube aids thatof the other in producing useful modulation components in the loadcircuit.

In Fig. 1, the tubes 4 and 5 are connected in parallel with the outgoingcircuit, this being the type of connection to be used when the sidebands produced by modulation in the tubes 4 and 5 are in phase. Underthese conditions the side bands are impressed on the input circuit ofthe tube 6 in phase addition. The output circuit of the tubes 4 and 5 isconnected to the terminals of a potentiometer resistance 14 across whichthe amplifier tube 6 may be variably connected. The usual blockingcondenser 15 is included in circuit with the potentiometer 14 to preventthe fiow of direct current in the grid circuit of the tube 6. The waveresulting from the combination of the side bands produced in the tubes 4and 5, is amplified in the tube 6 from which the amplified wave is thentransmitted to the high frequency line 17 which is inductively coupledto the output of the tube 6 by means of a transformer 16.

In Fig. 2 a type of circuit is shown for use when the modulating tubes 4and 5 produce side bands 180 out of phase with each other. Under theseconditions, if the output connection described above were to be used,the side band amplitude would be reduced, perhaps to zero. In order tomake the side bands produced by the two modulating tubes additive ineifect, the outgoing or load circuit should be connected in seriesrelation with the modulating tubes instead of in parallel with them. Inthe arrangement shown, the anode of the speech amplifier tube 1 and theanode of the oscillator tube 5 are connected in series relation withrespect to the outgoing line through the induction coil winding 18.Space current is furnished for both tubes by means of the source ofcurrent 19 through the choke coil 20 which is desi ned to keep the sumof the space currents of the two tubes constant. As in the case of thesystem described in connection with Fig. l, the path of the oscillatortube for variation currents is closed through the speech amplifier tubeand the path of the speech amplifier tube is likewise closed through theoscillator tube, and consequently, modulation takes place in both tubes.The winding 21 in the input circuit of the amplifier tube 6 isinductively related to the winding 18, and the side bands produced inthe tubes 4.- and 5 are combined in an additive sense and are amplifiedin the tube 6, from which the amplified wave is transmitted to the highfrequency line 17, as before.

Fig. 3 shows a modification of the system described in connection with Fig. 2 by means of which plate currents of different potentials may besupplied to the tubes 4 and 5. This modification may be substituted forthe portion of the system included within the dotted lines of Fig. 2. Inthis case, plate current is supplied to the speech amplifier tube 4 froma source of current 22 through a choke coil 23, and the primary of aninduction coil 24. Plate current is supplied to the oscillator tube 5from a source of current 25 through a choke coil 26 and the primary of atransformer 27. A blocking condenser 28 is provided between the primarywindings of transformers 2 1 and 27 to prevent the flow of directcurrent from either of the sources 22 or 25 through more than one platecircuit. The secondary windings of the transformers 24 and 27 areconnected in the input circuit of the amplifier tube 6, in which thecombined side bands are amplified before being transmitted to the line.

lVhile for the purpose of illustration, the invention has been describedin connection with a carrier signaling system, it will be understoodthat it is equally applicable to radio signaling systems.

The invention may also be embodied in forms other than those hereinshown and described without departing in any way from the spirit of theinvention, the scope of which is defined in the appended claims.

lVhat is claimed is 1. A transmission system comprising a source of lowfrequency signals, a vacuum tube for amplifying said signals, anoscillator serving as a source of high frequency oscillations, means formodulating said high frequency oscillations in accordance with said lowfrequency signals in both said amplifying tube and said oscillator, atransmission circuit, means for impressing the side bands produced .bymodulation in both of said modulating means upon said circuit in likephase, and a vacuum tube in said transmission circuit for amplifying theside bands impressed thereupon.

2. In a transmission system, a modulator comprising a three-elementvacuum tube for amplifying signal currents and a three-elementoscillator tube for generating a high frequency wave, said tubes havingtheir grid circuits independent of each other, coupling means betweenthe anodes causing modulation to take place in both tubes, and anoutgoing circuit cumulatively associated with the anodes of said tubeswith respect to the modulated waves.

3. In a transmission system, a modulator comprising a speech amplifiertube and an oscillator tube, each having space discharge comprising aspeech amplifier tube and an os-- 'cillator tube each having spacedischarge electrodes, separate sources of space current therefor, meansin series with said sources of space current for keeping constant asregards signaling variations the total space current supplied to both ofsaid tubes and for impressing the product of each tube upon the other,whereby modulation takes place in both tubes, an outgoing circuit, andmeans for impressing modulation components from both of said tubesupon'savid circuit in like phase.

Ina signaling system, a modulator comprising a three-element vacuum tubefor amplifying signal currents and a three-element oscillator tube forgenerating a high frequency Wave, said tubes having their grid circuitsindependent of each other and their anodes coupled over a path of lowimpedance to waves of a frequency of said high frequency Wave and themodulation products to permit modulation in both tubes, and an out goingcircuit associated with the anodes of said tubes in additive phaserelation for the modulation products for conveying modulated waves. 7, r

6. A signaling system comprising a signal wave'amplifying device of thespace discharge type, a high frequency oscillation generating device ofthe space discharge type, means for impressing a normal space dischargepotential on each device independent of the normal impedance of theother, means for impressing the potential variations developed in eachdevice upon the discharge space of the other device, whereby modulationtakes place in both devices, an outgoing circuit, and means forimpressing modulation components from said amplifying and generatingdevices upon said circuit in additive phase relation.

7 A signaling system comprising a vacuum tube of the audion type foramplifying signaling currents, an oscillator tube of the audion type forgenerating a high frequency Wave, a two-winding transformer having onewinding in circuit with the anode of said amplifier tube and the otherwinding in circuit with said oscillator tube, circuit means associatedwith said transformer and said tubes causing modulation to take place inboth tubes, and an outgoing circuit cumulatively.

associated with" the anodes of said tubes with respect to the modulatedwaves.

8. In a signaling system, a modulator comprising a speech amplifier tubeand an oscillator tube, each having space discharge EUGENE PETERSON,

electrodes, separate sources of space current therefor, a transformerhavmg one wmding

